High-power mode-locked laser systems are presently used in a variety of applications, such as multi-photon microscopy and device manufacturing. Presently, three types of high power, mode-locked laser systems are commonly available for these applications: thin disk laser systems, chirped pulse fiber amplifier systems and bulk laser systems. Thin disk laser systems are a diode pumped solid state laser system which includes a thin layer of active gain material positioned on a heat sink. A pump signal from a diode pump source is incident multiple times on the active gain material, which produces an output signal in response thereto. Historically, disk laser systems have been capable of producing high average powers. However, disk laser systems have been largely incapable of reliably producing output signals having pulse widths of less than about 500 femtoseconds (hereinafter “fs”) and at high average power and high repetition rates. Further, disk laser systems require a complex and expensive optical pumping configuration and thermal management system. Due to peak power limitations, fiber based high power, mode-locked lasers require an oscillator and a chirped pulse amplifier which includes stretching the pulse prior to amplification and then subsequent compression after amplification, thus adding cost and complexity to the system.
In contrast, bulk high power, mode-locked laser systems use optical crystals, such as Yb:YAG, Yb:CALGO, Yb:KYW or Yb:KGW, as the gain material. While prior art bulk high power mode-locked laser systems have proven useful in the past, a number of shortcomings have been identified. Often, the high power optical pumping of the optical crystal results in one or more undesirable thermal effects within the optical crystal. For example, one or more thermal lenses may be created within the optical crystal, thereby reducing the output power of the laser system. Typically, the average output power of these prior art bulk laser systems is less than about 15 W. FIG. 1 shows graphically the range wherein a continuous wave mode-locked (CW-ML) signal is outputted from the laser within prior art laser cavities as a function of average output power versus average pump power from the pump source. As shown, the narrow CW-ML regime is terminated by the undesirable instability regime. As such, operations or systems that require a CW-ML signal are restricted to relatively low optical average power applications. In addition, presently available bulk high-power mode-locked laser systems tend to be complex systems requiring multiple pump sources, complex thermal management systems, and the like.
Thus in light of the foregoing, there is an ongoing need for a simple, low cost high-power mode-locked laser system capable of producing short pulses at high average powers. There is a further need for a simple, low cost high-power mode-locked laser system capable of producing sub 200 fs pulse durations with average powers of more than 20 W. Further, there is an ongoing need for a simple, low cost high-power mode-locked laser system capable of producing these short pulse durations and high average powers at sufficient repetition rates for applications. Further, there is a need for a simple, low cost high-power mode-locked laser system with an extended CW-ML range for ease of manufacturing and robustness.